Nanowire Thermoelectrics

Thermoelectric materials generate electricity by extracting heat from a heat gradient. The best commercially available thermoelectrics have a figure of merit of ZT ~ 1, corresponding to an energy conversion efficiency of about 10% of the Carnot value. Whereas this relatively low efficiency limits thermoelectrics to niche applications, a significant increase in efficiency would have substantial economic impact. For instance, an effective thermoelectric may be used to partially recycle waste heat from the exhausts of car engines, potentially leading to significantly improved gas mileage. Thermoelectrics can also be used for silent refrigerators that have no compressor or refigerant.

We recently predicted that the efficiency of thermoelectric energy conversion can approach the Carnot efficiency in materials with the following properties:

• Electron transport is limited to a narrow energy band that coincides with the energy where the Fermi function in the hot reservoir equals that of the cold reservoir.
• Weak electron-phonon coupling.

Under these conditions, electrons can be in "energy-specific equilibrium" in spite of the presence of a heat gradient, and heat can be used to create electric current almost reversibly (without "friction").

The above conditions can in principle be fulfilled at low temperatures (where electron-phonon coupling is suppressed) in one-dimensional semiconductor nanowires with a built-in energy filter, such as a double-barrier resonant tunneling structure.

Project goals:

1. Proof-of-principle experiments demonstrating high thermoelectric efficiency in single nanowires at cryogenic temperatures.
2. Exploration of the potential of this concept for applications around room temperature.

Key Researchers at UO
Dr. Ann Persson
Eric Hoffmann

Collaborators
Dr. Tammy Humphrey, Geneva
Lars Samuelson, Lund University , Sweden
Mark O'Dwyer, University of Wollongong , Australia
Linus Fröberg, Lund University , Sweden

H. Linke, T.E. Humphrey and M. O'Dwyer: Energy-specific equilibrium in nanowires for efficient thermoelectric power generation. Proceedings of Symposium F at the MRS Fall Meeting 2005

M. O'Dwyer, T. E. Humphrey and H. Linke: Concept study for a high-efficiency nanowire-based thermoelectric. Submitted to Nanotechnology. Preprint at cond-mat/0601110

T. E. Humphrey and H. Linke: Reversible Thermoelectric Nanomaterials. Phys. Rev. Lett. 94 096601 (2005)

T. E. Humphrey and H. Linke: Quantum, cyclic, and particle-exchange heat engines. Physica E 29 (2005)

T.E. Humphrey and H. Linke: Reversible Quantum Brownian Heat Engines for Electrons. Phys. Rev. Lett. 89, 116801 (2002)

News Coverage and Popular Science Reports

Putting brownian motion to work (Nature Research Highlights, 30 August 2002)

A New Kind of Equilibrium (Phil Schewe and Ben Stein in APS Physics News Update 727 #1, April 14, 2005)
Nanomaterials draw electricity from heat (Philipp Ball for Nature Materials News, 24 March 2005)
Nanotechnology Now (April 5, 2005)

Recent Presentation

MRS Fall Meeting 2005 (Symposium F, invited)

Funding
Office of Naval Research (ONR) and ONR Global
The Australian Research Council

Links
Hi-Z Technology: Resource page for thermoelectrics R&D http://www.zts.com
Shakouri lab, UCSC http://quantum.soe.ucsc.edu/
Shi lab, University of Texas at Austin http://www.me.utexas.edu/~lishi/

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